The invention provides an apparatus for treating a wafer manufactured from semiconducting material, the apparatus comprising a first and a second housing part arranged for movement away from and towards each other, the two housing parts in a closed position, moved together, bounding a treatment chamber, at least one gas feed channel being provided in the first and/or second housing part which opens into the treatment chamber, the first and the second housing part around the treatment chamber being provided with a first and second boundary surface respectively, while in the closed position a gap is present between the first and the second boundary surface for discharging the gas fed into the treatment chamber in radially outward direction.
Such apparatus is known from Dutch patent application 103538 in applicant""s name. The apparatus described is intended for performing a temperature treatment on a wafer manufactured from semiconducting material. The temperature treatment comprises, for instance, the steps of heating up a wafer within a short time, which wafer is subsequently held at a desired treatment temperature during a treatment period, for instance for annealing a doping. During this treatment period, a treatment gas may also be fed to the wafer, for instance for depositing material onto the wafer or etching material therefrom. The dimensions of the structures created on or in the wafer and the sharpness of the boundary surfaces between the structures and the bulk of the semiconducting material require a precision in the nanometer range. Greater variations may already inhibit or even impede the desired operation of the structures formed by the treatment.
Apparatuses for performing such temperature treatment on a wafer are already known in various other versions, for instance apparatuses where the wafer is irradiated by infrared lamps, or apparatuses where the wafer is placed directly on a temperature treatment surface, such as a heated plate. The drawback of these apparatuses is that the heat transfer between the wafer and the temperature treatment means of the apparatus is not uniform. This may lead to undesired effects. Thus, the non-uniform heat transfer may effect local overheating and/or underheating in the wafer, causing tensions in the wafer. Relaxation of these tensions results in dislocations and other defects in the crystalline semiconducting material of the wafer. These defects can degrade the electric properties of the material such that it no longer meets the desired specifications and becomes unusable for the intended application. In the second place, the heat transfer affects the course of the temperature-sensitive wafer treatment steps such as the deposition of material or the annealing of a doping introduced. Due to a non-uniform heat transfer, the temperature of the wafer to be treated is not uniform. Accordingly, during the treatment, the treatment period on some parts of the wafer is too short or too long, as a consequence of which the material is undertreated or overtreated respectively at those locations. Thus, at those locations of the wafer, this treatment does not lead to the desired electric and/or material properties, due to the non-uniform temperature of the wafer, so that in this way, too, the wafer may become unsuitable for further use.
The problems of a non-uniform heat transfer are avoided in the apparatus from Dutch patent 103538. To that end, the apparatus comprises a first and a second housing part, arranged for movement away from and towards each other. The two housing parts are brought to a specific treatment temperature. In fact, the temperature for the two housing parts may be different. The wafer to be treated is enclosed between the two housing parts in a treatment chamber. This involves the absence of mechanical contact between the two housing parts relative to each other. A gap between two boundary surfaces of the housing parts is sealed by a gas flowing radially outwards over the entire circumference and coming from the treatment chamber. The volume of the treatment chamber encloses the wafer very tightly, so that the heat transfer between the wafer and the two housing parts is effected substantially by means of a uniform heat conduction and only for a small part by radiation. As a consequence, the wafer rapidly takes over the temperature of the two housing parts. The housing parts have a very great heat capacity in relation to the wafer, so that the temperature of the housing parts hardly changes through the heat loss due to the heat transfer to the wafer. In the closed position of the two housing parts, moved towards each other, the treatment chamber should be closed off from the environment of the apparatus, such that no contaminants from the ambient air of the apparatus can reach the treatment chamber. Indeed, it is important that during the treatment in the treatment chamber, the wafer surface cannot contact such contaminants. During the treatment, this contaminant may adhere to the wafer surface or be incorporated into a layer deposited by the treatment, and accordingly render the wafer unusable for subsequent treatment steps and desired applications.
In the above-described apparatus, gas from the treatment chamber is used for sealing the gap between the two housing parts. Such contactless seal is preferred to a mechanical seal, which involves a contact surface between the two housing parts. After all, a mechanical seal must typically be of complex design to establish a proper closure of the treatment chamber. In that case, for instance an O-ring should be used, which is compressed in the contact surface when the housing parts are moved towards each other. In addition, such seal is subject to wear caused by the mechanical contact at the contact surface. Due to this wear, the quality of the seal between the two housing parts deteriorates upon repeated use. Moreover, due to the wear, particles are released from the housing parts. These particles may end up in the treatment chamber and accordingly contaminate the wafer surface. Such mechanical seal becomes additionally complicated if the housing parts are each brought to a treatment temperature for the treatment. Expansion of the hot housing parts may cause gaps in the contact surface, whereby the seal is broken. Moreover, the proper sealing of the hot housing parts is cumbersome when an O-ring is used.
In practice, the contactless closing of the two housing parts, with the gap between the housing parts being sealed by gas from the treatment chamber, is not sufficient to bring the contamination level in the treatment chamber to a desired low level. Indeed, via the gap, contamination from the environment may diffuse in the treatment chamber. A second drawback of the described sealing of the gap between the two housing parts is that a treatment gas to be used in the treatment space flows away to the environment of the apparatus via the gap. Many gases that serve for performing a wafer treatment are toxic and/or highly flammable upon contact with air, for instance silane, disilane and phosphine. In that case, it is important to avoid possible contact of this treatment gas with the ambient air.
The object of the present invention is to provide a solution to these problems. According to the invention, an apparatus of the type described in the preamble is characterized in that in at least one of the two boundary surfaces, there is provided a first groove connected to gas discharge means, while in at least one of the two boundary surfaces, there is provided a second groove connected to gas feed means, both the first and the second groove extending substantially along the circumference of the treatment chamber, the first groove being located radially within the second groove, and, in use, the pressure created by the gas feed means being such that from the second groove, gas flows both in radial inward and in radial outward direction in the gap between the first and the second boundary surface.
In use, a wafer is introduced into the treatment chamber between the two housing parts. Gas flowing through the gap is discharged via the first groove by the gas discharge means, while via the second groove, gas is fed to the gap by the gas feed means. The gas discharged via the first groove comes from the at least one gas feed channel which opens into the treatment chamber, and may further comprise a portion of the gas from the second groove. Thus, the gap is sealed by the gas streams, so that contamination from the environment can hardly diffuse to the treatment chamber.
The gas fed to the second groove by gas feed means flows from the second groove through the gap between the two housing parts in radially inward as well as radially outward direction. In this manner, gas from the treatment chamber is directly discharged by the gas discharge means connected to the first groove. The gas fed to the second groove by the gas feed means provides for the desired sealing of the gap outside the circumference of the first groove. The effect thus achieved is that the treatment chamber is properly separated from the environment by the gas flowing from the gas feed means. It is observed that the first and second boundary surfaces do not necessarily extend parallel to the treatment chamber. The two housing parts may, for instance, have mating cylindrical forms, with the two boundary surfaces extending along the outer wall of the inner cylindrical form and the inner wall of the outer cylindrical form. Also, the boundary surfaces may, for instance, extend along a section of a conical surface.
In use of the apparatus, the Pxc3xa9clet number in the gap located radially outside the second groove is preferably greater than 10, the Pxc3xa9clet number Pe being defined by the following formula:   Pe  =            v      ·      L        D  
wherein v is the gas flow rate in the gap, L is the length of the gap viewed in flowing direction, and D is the diffusion coefficient of a contamination in the gas fed by the gas feed channels. At this Pxc3xa9clet number in the gap, diffusion of a contamination from the environment to the treatment chamber via the gap is very slight, so that a desired low contamination level is reached in the treatment chamber. This Pxc3xa9clet number can in most cases be achieved by taking a gas flow rate in the gap of the radially outwardly flowing gas of minimally 1 centimeter per second.
In a preferred embodiment, in use, the pressure created by the gas discharge means is such that substantially all the gas fed into the treatment chamber is discharged via the first groove. Thus, contact between ambient air and the gas fed into the treatment chamber is avoided, which is necessary in respect of some treatment gases.
Preferably, in an open, moved-apart position, the two housing parts keep clear an interspace between the first and second boundary surfaces for loading and unloading the wafer by means of wafer transport means. In this manner, the wafer to be treated can be moved between the two housing parts and discharged again after a treatment.
In a further elaboration of the preferred embodiment, gas feed channels are provided in the first and/or second housing part, opening into the treatment chamber to form a gas bearing for contactlessly supporting the wafer in the treatment chamber. In use, the gas bearing keeps the wafer over its entire wafer surface at an equal distance between the housing parts and may thus compensate for any deviations in the flatness of the wafer. This renders the heat transfer from the housing parts to the contactlessly supported wafer highly uniform.
During the loading of the wafer, the position of the wafer transport means relative to at least one of the housing parts is preferably such that the gas bearing takes the wafer from the wafer transport means in the treatment chamber when the two housing parts move towards each other from the open position. Thus, the wafer in the treatment chamber can be brought into the gas bearing, so that no mechanical contact between the wafer and the housing parts takes place. This avoids the occurrence of a non-uniform heat transfer before the two housing parts are in their closed position. Further, at least one of the two boundary surfaces of one of the two housing parts may be provided with a number of wafer transport means receiving grooves which incorporate the wafer transport means when the two housing parts are in their closed position. In this manner, the wafer transport means can remain behind adjacent the wafer after the wafer has been taken in the treatment chamber by the gas bearing. This enables the wafer, after treatment, to be rapidly received by the transport means for transporting the wafer from the treatment chamber to, for instance, a subsequent treatment apparatus. This further provides the possibility of rapidly introducing a next wafer to be treated into the treatment chamber, which adds to the productivity of the apparatus.
In the preferred embodiment, the wafer transport means receiving grooves extend in radial direction, the second groove being interrupted at the location of each wafer transport means receiving groove. In spite of the fact that the second groove is interrupted, there may still be created a gas barrier at the location of the wafer transport means receiving groove in that, in accordance with a further elaboration of the invention, gas feed means preferably open into the wafer transport means receiving grooves, with the wafer transport means receiving grooves at a radially inwardly located part being in fluid connection with the first grooves. Thus, the wafer transport means receiving grooves are also sealed by gas which, in use, flows from the gas feed means. That gas can be discharged via the first groove and, by flowing radially outside to the environment, via the wafer transport means receiving grooves themselves. Thus, no contamination can diffuse in the treatment chamber via the wafer transport means receiving grooves during use of the apparatus.
In a preferred embodiment, the wafer transport means substantially comprise a transport ring provided with a number of support fingers, the transport ring having a diameter greater than the outer circumference of the two housing parts, the support fingers being connected to the transport ring and extending radially in the direction of the center of the transport ring, such that the ends of the support fingers jointly support a circumferential edge of the wafer. In use, the two housing parts can move towards each other within the transport ring, with the wafer being taken from the transport ring, to start the treatment of the wafer. After the treatment, the housing parts can subsequently move apart, with the wafer being placed on the transport ring. After that, a robot arm can remove the transport ring with wafer in lateral direction from the apparatus, and move it, for instance, to a next treatment apparatus.
In use, the first and the second housing part, in operation, have a substantially constant temperature, while in the closed position of the two housing parts, the distance between the wafer enclosed in the treatment space and the two housing parts is so small, that the heat transfer between the two housing parts and the wafer is substantially effected by heat conduction. Thus, the wafer can rapidly take over the temperature of the housing parts, the heat transfer being uniform.
The gas feed means can be provided with an inert gas source, for instance a nitrogen source. An inert gas is harmless if it is released in the environment via the gap between the first and second boundary surfaces.
The gas feed channels for the gas bearing may likewise be connected to an inert gas source. During the treatment, this prevents the wafer from entering into undesired chemical or physical reactions with the gas fed for the gas bearing.